We will measure how reading by observers with normal and low vision depends on the stimulus properties of text. The stimulus properties of text that are necessary for normal observers to read are defined to be the visual requirements of reading. Our research has three primary goals: 1) to measure the visual requirements of reading under conditions that are relevant to low vision; 2) to develop simple tests of visual capacity that can predict reading performance of low-vision observers; and 3) to discover the influence on reading performance of stimulus properties, opthalmic disorder, acuity deficit and field loss for low-vision observers. We will use psychophusical methods in five series of exerpiments. First we will discover the visual requirements of normal reading, with special emphasis on contract and spatial frequency. We will also measure the visual requirements of letter, word, and picture recognition. Secondly, we will seek to develop improved means for measuring contrast sensitivity, based on recognition rather than detection, to quantify the visual capacityes of low-vision observers. Thirdly, we will determine whether recognition tests of contrast sensitivity and knowledge of the visual requirements of normal reading can be used together to predict reading performance of low-vision observers. Fourthly, we will measure effects of several special factors of low-vision reading--glare, contrast reversal, wavelength, and defocus. Finally, we will test hyptheses that attempt to explain psychphysical properties of reading in terms of known properties of pattern vision. The research will be useful in three ways: 1) improved uonderstanding of the sensory constrains of normal reading; 2) the development of systematic techniques for testing low-vision capacity, with the aim of specifying image properties required of an appropriate reading aid; and 3) in establishing necessary stimulusl characteristics for new low-vision reading aids.